As a cooling device for a piston of a conventional internal combustion engine, there is known an oil jet device in which a nozzle pipe providing a cooling oil channel held in fluid communication with an oil passageway in the internal combustion engine extends to the back of the piston, and oil is ejected from the nozzle pipe. Japanese Utility Model Laid-Open No. Sho 54-164328 (JP '328) discloses a technology wherein a filter for filtering the oil is disposed in the oil channel to prevent the oil ejection port from being clogged. Japanese Patent Laid-Open No. 2011-94519 (JP '519) reveals a technology wherein a check valve is provided to keep the oil pressure in the oil channel at a level equal to or higher than a predetermined value for thereby achieving the target aiming ability of the ejection (e.g., the ejection of the oil toward an area to be cooled).